Vehicle control method and vehicle control system

ABSTRACT

A vehicle control method of performing automatic braking for automatically braking a vehicle or alarm output, depending on a possibility of a collision between the vehicle and an obstacle, includes: cancelling the automatic braking or the alarm output, when an accelerator operation amount is equal to or larger than a predetermined threshold value, during the automatic braking or the alarm output, and cancelling the automatic braking or the alarm output, when a given cancellation condition is satisfied under a situation where the accelerator operation amount of the vehicle is smaller than the predetermined threshold value, during the automatic braking or the alarm output.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a vehicle control method and a vehicle controlsystem.

2. Description of Related Art

A brake control system for a vehicle is known which automatically puts abrake on the vehicle, depending on a risk of collision between thevehicle and an obstacle. The vehicular brake control system includes acollision determining means for determining whether the risk ofcollision between the vehicle and the obstacle is high, automaticbraking means for automatically generating braking force by controllinga brake system of the vehicle, when the collision determining meansdetermines that the risk of collision between the vehicle and theobstacle is high, and an automatic braking cancelling means for stoppingautomatic generation of the braking force by the automatic brakingmeans, when the frequency at which the accelerator pedal of the vehicleis operated by the driver of the vehicle is equal to or higher than apredetermined value (see, for example, Japanese Patent ApplicationPublication No. 2012-224119 (JP 2012-224119 A)).

However, in the vehicular brake control system as described in JP2012-224119 A, only the frequency of operation of the accelerator pedalof the vehicle by the driver, or the duration of the operation, is takeninto consideration, and automatic braking may not be cancelled in such amanner that better suits the intention of the driver.

SUMMARY OF THE INVENTION

The invention provides a vehicle control method and a vehicle controlsystem, with which automatic braking, or the like, is cancelled in sucha manner that better suits the intention of the driver.

A vehicle control method of performing automatic braking forautomatically braking a vehicle or alarm output, depending on apossibility of a collision between the vehicle and an obstacle,according to a first aspect of the invention, includes: cancelling theautomatic braking or the alarm output, when an accelerator operationamount is equal to or larger than a predetermined threshold value,during the automatic braking or the alarm output, and cancelling theautomatic braking or the alarm output, when a given cancellationcondition is satisfied under a situation where the accelerator operationamount of the vehicle is smaller than the predetermined threshold value,during the automatic braking or the alarm output.

A vehicle control system according to a second aspect of the inventionincludes a sensor that detects a condition of an obstacle around avehicle, an accelerator pedal position sensor that detects an operationamount of an accelerator pedal, and an ECU that outputs a signal thatrequests automatic braking for automatically braking the vehicle orgeneration of an alarm, based on the condition of the obstacle, andstops output of the signal when the operation amount of the acceleratorpedal is equal to or larger than a first threshold value, or when theoperation amount of the accelerator pedal is smaller than the firstthreshold value, and a given first condition is satisfied.

According to the above aspects of the invention, it is possible tocancel automatic braking, or the like, in such a manner that bettersuits the intention of the driver.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the invention will be described below withreference to the accompanying drawings, in which like numerals denotelike elements, and wherein:

FIG. 1 is a view schematically showing the configuration of a vehiclecontrol system according to one embodiment of the invention;

FIG. 2 is a view showing one example of processing implemented by acollision determination ECU of the vehicle control system of FIG. 1;

FIG. 3 is a view showing one example of patterns of changes in a targetcontrol value of an automatic braking request when automatic braking iscancelled and when automatic braking is normally finished; and

FIGS. 4A and 4B are schematic views useful for explaining the overlappercentage; and

FIG. 5 is an explanatory view showing one example of method ofdetermining a relaxed cancellation condition according to a tenthexample.

DETAILED DESCRIPTION OF EMBODIMENTS

One embodiment of the invention will be described in detail withreference to the accompanying drawings.

FIG. 1 schematically shows the configuration of a vehicle control system1 according to one embodiment of the invention. The vehicle controlsystem 1 includes a collision determination ECU (Electronic ControlUnit) 10. Like other ECUs, the collision determination ECU 10 mainlyconsists of a microcomputer, or the like.

A sensor 12 is connected to the collision determination ECU 10. Thesensor 12 detects conditions of an obstacle (typically, a vehicle) infront of the vehicle, using radio waves (e.g., millimeter waves), lightwaves (e.g., laser), or ultrasonic waves, as detection waves. The sensor12 detects information indicating the relationship between the obstacleand the vehicle at predetermined intervals. The information indicatingthe relationship between the obstacle and the vehicle includes, forexample, the velocity of the obstacle relative to the vehicle on whichthe sensor 12 is installed, the distance between the obstacle and thevehicle, and the direction (lateral position) of the obstacle as viewedfrom the vehicle. The sensor 12 may be a millimeter-wave radar. Forexample, the millimeter-wave radar may be an electronic scan typemillimeter-wave radar. The electronic scan type millimeter-wave radardetects the relative velocity of the obstacle, using the Dopplerfrequency (frequency shift) of radio waves, detects the distancerelative to the obstacle, using the delay time of reflected waves, anddetects the direction of the obstacle based on a phase difference ofreceived waves between two or more receiving antennas. The detectiondata is transmitted from the sensor 12 to the collision determinationECU 10 at predetermined intervals. One or more of the functions (e.g.,the function of calculating the position of a forward obstacle) of thesensor 12 may be implemented by the collision determination ECU 10.

An image sensor may be used as the sensor 12. The image sensor includesa camera including an image pickup device, such as CCD (charge-coupleddevice) or CMOS (complementary metal oxide semiconductor), and an imageprocessor, and is operable to recognize an image representing conditionsof an obstacle. The camera of the image sensor may be a stereo camera.The image sensor detects conditions of the obstacle, based on the resultof image recognition. More specifically, the image sensor detectsinformation indicating the relationship between the obstacle and thevehicle, for example, the velocity of the obstacle relative to thevehicle, and the information on the position of the obstacle withreference to the vehicle, at predetermined intervals. The positionalinformation of the obstacle may include information concerning theposition (distance) of the obstacle in the longitudinal direction of thevehicle, and information concerning the lateral position (or overlappercentage) of the obstacle in the lateral direction (width direction).The lateral position of the obstacle may be calculated based on thecenter of a group of pixels associated with the obstacle as viewed inthe lateral direction, or may be calculated as a range between thelateral position of the left end of the obstacle and the lateralposition of the right end thereof. The information (detection result)obtained by the image sensor may be transmitted to the collisiondetermination ECU 10 with a given frame period, for example. The imageprocessing function (e.g., the function of calculating the position of aforward obstacle) of the image processor of the sensor 12 may beimplemented by the collision determination ECU 10. The sensor 12 mayinclude two or more types of the sensors as described above.

Various types of electronic components in the vehicle are connected tothe collision determination ECU 10, via an appropriate bus, such as CAN(controller area network). In the embodiment shown in FIG. 1, a brakeECU 20 that controls a brake system (not shown), engine ECU 22 thatcontrols an engine (not shown), meter ECU 24, body ECU 26, drivermonitoring camera 28, and a steering ECU 30 are connected to thecollision determination ECU 10.

The driver monitoring camera 28 includes a color or infrared-sensitiveCCD (charge-coupled device) sensor array, for example, and is located ata position (e.g., on a steering column) where an image of the driver'sface can be captured. The driver monitoring camera 28 has an imageprocessing function, and detects various conditions (e.g., the directionof the driver' face, such as the driver's failure to keep his/her eyeson the road, a condition of slumber, and a condition of wakefulness).Any desired logic may be employed for detecting the face direction, andpattern matching, or the like, may be used. Similarly, any desired logicmay be employed for detecting a condition of slumber or wakefulness, andthe opening of the eyes, the frequency of yawns, etc. may be taken intoconsideration. The driver monitoring camera 28 may cooperate withanother biological sensor (such as a body surface temperature sensor) todetect the condition of slumber or wakefulness. The image processingfunction (e.g., the function of detecting the driver's failure to keephis/her eyes on the road, or the condition of slumber) of the drivermonitoring camera 28 may be implemented by the collision determinationECU 10.

An accelerator pedal position sensor 23 that detects the amount ofoperation of the accelerator pedal is connected to the engine ECU 22.The collision determination ECU 10 obtains information concerning theaccelerator pedal position (the amount of operation of the acceleratorpedal), via the engine ECU 22, or the like. However, the method by whichthe collision determination ECU 10 obtains information concerning theamount of operation of the accelerator pedal is not limited to thismethod. For example, the accelerator pedal position sensor 23 may beconnected to the collision determination ECU 10, and the collisiondetermination ECU 10 may obtain the information concerning the amount ofoperation of the accelerator pedal, directly from the accelerator pedalposition sensor 23.

A steering angle sensor 31 that detects the steering angle of thesteering wheel is connected to the steering ECU 30. The collisiondetermination ECU 10 obtains information concerning the steering angle(namely, information from the steering angle sensor 31), via thesteering ECU 30. However, the method by which the collisiondetermination ECU 10 obtains information concerning the steering angleis not limited to this method. For example, the steering angle sensor 31may be connected to the collision determination ECU 10, and thecollision determination ECU 10 may obtain the information concerning thesteering angle, directly from the steering angle sensor 31.

FIG. 2 illustrates one example of processing implemented by thecollision determination ECU 10. The processing illustrated in FIG. 2 maybe repeatedly executed at predetermined intervals, during execution ofautomatic braking, for example. The automatic braking may be startedwhen an automatic braking condition is satisfied. The automatic brakingcondition, which is a condition that is satisfied when automatic brakingshould be carried out, may be set in any manner. For example, incollision avoidance control for avoiding collision with a forwardobstacle, a length of time it takes for the vehicle to collide with theforward obstacle, or TTC (Time to Collision), may be calculated, and theautomatic braking condition may satisfied when the calculated TTCbecomes shorter than a predetermined value (e.g., 1.5 sec.). In thiscase, the collision determination ECU 10 may calculate the TIC for theforward obstacle located within a predetermined angular range (orlateral position), based on the result of detection from the sensor 12,and may determine that the automatic braking condition is satisfied whenthe calculated TTC becomes shorter than the predetermined value (e.g.,1.5 sec.). The TTC may be obtained by dividing the distance relative tothe forward obstacle, by the relative velocity against the forwardobstacle. In automatic driving control, an automatic braking conditionmay be satisfied when the magnitude of the deceleration required to keepthe distance between a forward vehicle and the vehicle equal to a lowerlimit value exceeds a predetermined value, for example.

Also, the automatic braking condition may be satisfied when it isdetermined that collision with a forward obstacle (such as a vehicle)cannot be avoided. Namely, the condition may be satisfied when thepossibility of collision with the forward obstacle is equal to or higherthan a predetermined level (in this case, 100%). A great variety ofmethods for determining whether collision with a forward obstacle cannotbe avoided are widely known in the field of pre-crash safety, and any ofthese methods may be employed. For example, the relative velocity atwhich collision can be avoided may be calculated in advance, for eachTTC, and a collision unavoidableness determination map may be preparedbased on the calculated relative velocities. In this case, the collisiondetermination ECU 10 may determine whether collision with a forwardobstacle cannot be avoided, referring to the collision unavoidablenessdetermination map, based on the relative velocity against the forwardobstacle, and the TTC. More specifically, the deceleration G (m/s²) anddeceleration velocity V (m/s) measured t seconds after automatic brakingis started have the following relationships where G_(MAX) (m/s²) is themaximum velocity, and J (m/s³) is the deceleration gradient: G=Jt,V=J×t²/2 when t≤G_(MAX)/J, G=G_(MAX), V=G_(MAX)²/(2J)+G_(MAX)(t−G_(MAX)/J) when G_(MAX)/<t. In this case, the collisionunavoidableness determination map may be created, by regarding therelative velocity larger than the deceleration velocity V measured tseconds after start of automatic braking, as a relative velocity atwhich collision cannot be avoided. In another method, the relativedistance may be obtained by integrating the deceleration velocity V, anda collision unavoidableness determination map may be created, using therelative distance as a parameter. In a further method, the acceleration,etc. of the forward obstacle may be taken into consideration, for use ina further complicated algorithm.

In step S200, the latest information is obtained from various sensors.For example, information from the sensor 12, information concerning theaccelerator pedal position (the amount of operation of the acceleratorpedal), information from the steering angle sensor 31, and others, maybe obtained. The obtained sensor information, which is needed indetermining operations as will be described later, varies depending on adetermination method employed (a relaxed cancellation conditionemployed).

In step S202, it is determined whether an automatic braking terminationcondition is satisfied. The automatic braking terminal condition is acondition for normally finishing automatic braking. The automaticbraking termination condition may be any condition, but may be satisfiedin the case where a collision is detected, the case where the vehiclebody speed becomes equal to 0 km/h, the case where TTC exceeds 1.5 sec.,or the case where an automatic braking request (step S212) has beengenerated for a predetermined period of time (e.g., 3 sec.) or longer.If the automatic braking termination condition is satisfied, the controlproceeds to step S204. If not, the control proceeds to step S206.

In step S204, automatic braking is finished. To finish automaticbraking, the collision determination ECU 10 may stop generating theautomatic braking request (step S212) that had been generated until thelast computation cycle. At this time, the automatic braking request maynot be immediately stopped, but the automatic braking request may becontinuously generated in such a manner that a target control value isreduced at a given rate to a given value close to 0, and then kept atthe given value close to 0, so as to prevent rapid change of brakingforce. The given rate at which the target control value is reduced atthis time may be larger a given rate (step S210) used when automaticbraking is cancelled. The given value close to 0 may correspond to theminimum braking force required to keep the vehicle in a stopped state.In this manner, if the operation to finish automatic braking iscompleted in step S204 (namely, if the automatic braking request isstopped, or the target control value becomes equal to 0), the processingconcerning this time's automatic braking ends.

In step S206, it is determined whether a normal cancellation conditionis satisfied, based on information concerning the accelerator operationamount. The normal cancellation condition is satisfied when theaccelerator operation amount is equal to or larger than a predeterminedfirst threshold value Th1. The predetermined first threshold value Th1corresponds to the lower limit of the range of accelerator operationamount within which the driver has a clear intention of accelerating thevehicle, and may be set by experiment, or the like. For example, thepredetermined first threshold value Th1 may be a value around 60%. Ifthe accelerator operation amount is equal to or larger than thepredetermined first threshold value Th1, the control proceeds to stepS210. If not, the control proceeds to step S208.

In step S208, it is determined whether a relaxed cancellation conditionis satisfied, based on specified information. The relaxed cancellationcondition is a condition different from the normal cancellationcondition determined in the above step S206, and can be satisfied evenwhen the accelerator operation amount is smaller than the predeterminedfirst threshold value Th1. The relaxed cancellation condition may besatisfied when a specified collision avoidance operation of the driveris detected, under a situation where the accelerator operation amount issmaller than the predetermined first threshold value Th1. The driver'soperation, which is performed so as to avoid collision with a forwardobstacle, may be arbitrarily set or defined. The specified collisionavoidance operation of the driver is typically realized by one or acombination of an operation performed on the accelerator pedal foracceleration, and a steering operation for changing the travellingdirection. Some specific examples of collision avoidance operations(relaxed cancellation conditions) will be described later. If therelaxed cancellation condition is satisfied, the control proceeds tostep S210. If not, the control proceeds to step S212.

In step S210, automatic braking is cancelled. Namely, if the normalcancellation condition or relaxed cancellation condition is satisfiedafter the automatic braking condition is satisfied, automatic braking iscancelled. If the normal cancellation condition or relaxed cancellationcondition is satisfied, in the control cycle in which the automaticbraking condition is satisfied for the first time, automatic braking maynot be started, or automatic braking may be once started. In the lattercase, automatic braking may be started while it is not determinedwhether the normal cancellation condition or relaxed cancellationcondition is satisfied, in the control cycle in which the automaticbraking condition is satisfied for the first time, and then, the controlroutine of FIG. 2 may be started. The automatic braking may be cancelledby stopping the automatic braking request (step S212) that had beengenerated until the last cycle. At this time, the automatic brakingrequest may not be immediately stopped, but the automatic brakingrequest may be continuously generated in such a manner that the targetcontrol value is reduced at a given rate to 0, so as to prevent rapidchange of the braking force. Thus, if cancellation of automatic brakingis completed in step S210 (namely, if the automatic braking request isstopped, or the target control value becomes equal to 0), the processingconcerning this time's automatic braking ends.

In step S212, the automatic braking request is generated to the brakeECU 20, so as to execute automatic braking. The automatic braking iscontrol for increasing the wheel cylinder pressure of each wheel, undera situation where the brake pedal is not operated by the driver.Accordingly, the target control value used at the time of automaticbraking is determined based on a factor or factors other than theoperation amount of the brake pedal. The target control value may be afixed value, or a variable value. Even in the case where the targetcontrol value is a fixed value, the fixed value may change with time(see FIG. 3). Also, the target control value may be varied according tothe vehicle speed obtained when automatic braking is started. The targetcontrol value may be any physical quantity, which may be, for example, adeceleration, hydraulic pressure, the rate of increase in the pressure,or the like. The target control value may be included in the automaticbraking request and supplied to the brake ECU 20, or may be supplied asan automatic braking request to the brake ECU 20.

According to the processing illustrated in FIG. 2, the normalcancellation condition that is satisfied when the accelerator operationamount is equal to or larger than the predetermined first thresholdvalue Th1 is used; therefore, automatic braking can be cancelled withhigh reliability, under the situation where the driver has a clearintention of accelerating the vehicle.

In this connection, even under the situation where the acceleratoroperation amount is smaller than the predetermined first threshold valueTh1, it may be preferable to cancel automatic braking, depending on thereliability of collision determination (the reliability with which theautomatic braking condition is determined), the degree of easiness toavoid collision (for example, it is relatively easy to avoid collisionwhen the overlap percentage of a forward obstacle and the vehicle islow), and the driver's operation to avoid collision. Accordingly, if thecollision determination ECU 10 is configured to uniformly apply only thenormal cancellation condition to cancellation of automatic braking,automatic braking may be undesirably continued even under a situationwhere automatic braking should be cancelled early, and may fail to fitwith the driver's feeling.

In this respect, according to the processing illustrated in FIG. 2, evenin the situation where the accelerator operation amount is smaller thanthe predetermined first threshold value Th1 (namely, where the normalcancellation condition cannot be satisfied), automatic braking can becancelled when the relaxed cancellation condition is satisfied. In thismanner, automatic braking is prevented from being continued, under thesituation where automatic braking should be cancelled early, thus makingit possible to achieve control that fits with the driver's feeling.

In the processing illustrated in FIG. 2, after automatic braking isstarted, it is always determined whether the normal cancellationcondition and relaxed cancellation condition are satisfied, unless theautomatic braking termination condition is satisfied. However, theperiod of determination of the normal cancellation condition and relaxedcancellation condition may be more restricted. For example, the normalcancellation condition and relaxed cancellation condition may bedetermined when the above-indicated TTC is within a predetermined range,for example. The predetermined range corresponds to a period withinwhich a collision avoidance operation is effective, and may be set byexperiment, or the like. For example, the predetermined range may be inthe range of 1.5 sec. to 0.4 sec. Also, the period of determination ofthe relaxed cancellation condition may not be the same as the period ofdetermination of the normal cancellation condition, but the period ofdetermination of the relaxed cancellation condition may be shorter thanthe period of determination of the normal cancellation condition, forexample. In this case, the period of determination of the relaxedcancellation condition may be fully included in the period ofdetermination of the normal cancellation condition, or a part of thedetermination period of the relaxed cancellation condition may not beincluded in the determination period of the normal cancellationcondition.

While the automatic braking termination condition is determined earlierthan the normal cancellation condition and the relaxed cancellationcondition, the order of determination may be set as desired. Forexample, the normal cancellation condition and relaxed cancellationcondition may be determined earlier, and then, the automatic brakingtermination condition may be determined. Similarly, the order ofdetermination of the normal cancellation condition and that of therelaxed cancellation condition may also be set as desired.

FIG. 3 shows one example of patterns of changes in the target controlvalue of the automatic braking request at the time when automaticbraking is cancelled and when automatic braking is normally finished. InFIG. 3, the pattern of change or waveform of the target control value atthe time when automatic braking is cancelled is indicated by the thicksolid line.

Initially, the case where automatic braking is finished (namely, thecase where automatic braking is normally finished) with neither of thenormal cancellation condition and the relaxed cancellation conditionbeing satisfied will be described. In the example shown in FIG. 3, theautomatic braking condition is satisfied at time t0, and the conditionwhere the automatic braking condition is satisfied continues until timet5; then, the automatic braking termination condition (see step S202 ofFIG. 2) is satisfied at time t5. In this case, at time t0, the targetcontrol value of the automatic braking request is set to a predeterminedvalue α1 that is slightly larger than 0. The predetermined value α1 maycorrespond to a value required to reduce or eliminate a backlash of abrake actuator (by releasing air, for example). Then, at time t1 thatcomes a given time after time t0, the target control value of theautomatic braking request is set to a predetermined value α2. Thepredetermined value α2 is set to such a value that produces light,gentle braking force. Namely, automatic braking may be performed suchthat the maximum braking force (predetermined value α3) is produced fromthe beginning; however, as shown in FIG. 3, light, gentle braking forcemay be produced at first, and then, the maximum braking force may beproduced. Namely, the automatic braking may include moderate braking(preliminary braking) executed prior to main braking. Then, at time t2that comes a given time after time t0, the target control value of theautomatic braking request is set to a predetermined value α3. Thepredetermined value α3 may correspond to the maximum braking force thatmakes it possible to avoid collision with a forward obstacle (orminimize damage caused by collision). The predetermined value α3 ismaintained until time t5. If the automatic braking termination conditionis satisfied at time t5, the target control value of the automaticbraking request is reduced at a given rate from the predetermined valueα3 to a predetermined value α4, and the predetermined value α4 ismaintained only for a given period of time (e.g., 2 sec.) from time t6.Then, the target control value is reduced down to 0 at time t7.

Next, the case where the normal cancellation condition or relaxedcancellation condition is satisfied during execution of automaticbraking, and the automatic braking is cancelled, will be explained. Inthe example shown in FIG. 3, the automatic braking condition issatisfied at time t0, and then, the condition where the automaticbraking condition is satisfied continues until time t3. Then, at timet3, the normal cancellation condition or relaxed cancellation condition(see steps S206, S208 of FIG. 2) is satisfied. In this case, the targetcontrol value varies in the same manner as described above until timet3. If the normal cancellation condition or relaxed cancellationcondition is satisfied at time t3, the target control value of theautomatic braking request is reduced at a given rate from thepredetermined value α3 to 0. The given rate may be lower than the givenrate used when the automatic braking termination condition is satisfied,as shown in FIG. 3.

Next, some examples of relaxed cancellation conditions will bedescribed. Each of the relaxed cancellation conditions of various typesas described below may be used alone, or any combination of two or morerelaxed cancellation conditions may be used. In this case, the relaxedcancellation conditions of various types are combined under an ORcondition, but may be combined under an AND condition when appropriate.

A relaxed cancellation condition according to one example (firstexample) is satisfied when the accelerator operation amount is equal toor larger than a predetermined second threshold value Th2(<predetermined first threshold value Th1), and the speed of depressionof the accelerator pedal (the rate of increase of the acceleratoroperation amount) is equal to or higher than a predetermined speed. Thisis because, in this case, it can be determined with high accuracy thatthe driver has an intention of accelerating the vehicle, even though theaccelerator operation amount does not reach the predetermined firstthreshold value Th1 (threshold value associated with the normalcancellation condition). The predetermined speed may correspond to thelower limit of the range within which the accelerator pedal depressionspeed can fall when the driver has an intention of accelerating thevehicle, and may be set by experiment, or the like. The predeterminedspeed may be a value within the range of 200 to 400 mm/sec., forexample. If this relaxed cancellation condition is used in step S208 ofFIG. 2, the information concerning the accelerator operation amount maybe obtained as sensor information in step S200.

A relaxed cancellation condition according to another example (secondexample) is satisfied when the direction of the driver's face changedfrom a condition where the driver fails to keep his/her eyes on theroad, to the front direction, and the accelerator operation amountincreased by a predetermined amount or more after (in particular,immediately after) the change of the driver's face direction. This isbecause, in this case, it can be determined that the driver noticed adanger, and promptly depressed the accelerator pedal by an increasedamount or depressed the accelerator pedal again (i.e., performed acollision avoidance operation). To depress the accelerator pedal by theincreased amount means further depression of the accelerator pedal, andto depress the accelerator pedal again means depression of theaccelerator pedal after the accelerator pedal is once released; both ofthe manners of depressing the accelerator pedal indicate that thedriver's intention is finally the intention of accelerating the vehicle,and that the accelerator operation amount is increased. Thepredetermined amount by which the accelerator operation amount increasedmay be 20%, for example. If this relaxed cancellation condition is usedin step S208 of FIG. 2, the information concerning the acceleratoroperation amount, and the information from the driver monitoring camera28, may be obtained as sensor information in step S200.

A relaxed cancellation condition according to another example (thirdexample) is satisfied when the direction of the driver's face changedfrom a condition where the driver fails to keep his/her eyes on theroad, to the front direction, and a specified steering operation wasperformed after (in particular, immediately after) the change of thedriver's face direction. This is because, in this case, it can bedetermined that the driver noticed a danger, and promptly performed thesteering operation (i.e., performed a collision avoidance operation).The specified steering operation may be an operation that results in achange of the steering angle by a predetermined degree or larger. Thepredetermined degree of turn of the steering wheel may correspond to thelower limit of the range of steering angle within which the vehicle canmove in the lateral direction by a distance corresponding to the widthof one vehicle (or the width of one lane or the width of an overlaprange between the forward obstacle and the vehicle), within a short time(for example, time corresponding to the current TTC, or a given fixedtime). The predetermined degree may be set by experiment, or the like.Also, the specified steering operation may be a steering operation thatresults in an increase of the accelerator operation amount. Also, thespecified steering operation may be determined in view of the steeringtorque or steering speed. Also, the specified steering operation may bedetermined in view of the steering direction, as in the case of a ninthexample as will be described later. When this relaxed cancellationcondition is used in step S208 of FIG. 2, the information concerning theaccelerator operation amount, and the steering angle information, may beobtained in step S200.

A relaxed cancellation condition according to another example (fourthexample) is satisfied when the driver's condition changed from acondition of slumber to a condition of wakefulness, and the acceleratoroperation amount increased by a predetermined amount or more after (inparticular, immediately after) the change of the driver's condition.This is because, in this case, it can be determined that the drivernoticed a danger, and promptly depressed the accelerator pedal by anincreased amount or depressed the accelerator pedal again (i.e.,performed a collision avoidance operation). The predetermined amount bywhich the accelerator operation amount increased may be 20%, forexample. If this relaxed cancellation condition is used in step S208 ofFIG. 2, the information concerning the accelerator operation amount, andthe information from the driver monitoring camera 28, may be obtained assensor information in step S200.

A relaxed cancellation condition according to another example (fifthexample) is satisfied when the driver's condition changed from acondition of slumber to a condition of wakefulness, and a specifiedsteering operation was performed after (in particular, immediatelyafter) the change of the driver's condition. This is because, in thiscase, it can be determined that the driver noticed a danger, andpromptly performed the steering operation (i.e., performed a collisionavoidance operation). The specified steering operation may be anoperation that results in a change of the steering angle by apredetermined degree or larger. The predetermined degree of turn of thesteering wheel may correspond to the lower limit of the range ofsteering angle within which the vehicle can move in the lateraldirection by a distance corresponding to the width of one vehicle (orthe width of one lane or the width of an overlap range between theforward obstacle and the vehicle), within a short time. Thepredetermined degree may be set by experiment, or the like. Also, thespecified steering operation may be a steering operation that results inan increase of the accelerator operation amount. Also, the specifiedsteering operation may be determined in view of the steering torque orsteering speed. Also, the specified steering operation may be determinedin view of the steering direction, as in the case of the ninth exampleas described later. When this relaxed cancellation condition is used instep S208 of FIG. 2, the information concerning the acceleratoroperation amount, and the steering angle information, may be obtained instep S200.

A relaxed cancellation condition according to another example (sixthexample) is satisfied when a specified steering operation is performedwithin a predetermined period of time (e.g., 2 sec.) after the automaticbraking condition is satisfied, and the accelerator operation amount isequal to or larger than a predetermined third threshold value Th3(<predetermined first threshold value Th1). This is because it can bedetermined that the driver performs a collision avoidance operation,based on the fact that the steering operation is performed within thepredetermined time after the automatic braking condition is satisfied.The predetermined third threshold value Th3 may be significantly lowerthan the predetermined threshold value Th2, and may be 30%, for example.Similarly, the specified steering operation may be a steering operationthat results in an increase of the accelerator operation amount. Also,the specified steering operation may be determined in view of thesteering torque or the steering speed. Also, the specified steeringoperation may be determined in view of the steering direction, as in thecase of the ninth example as will be described later.

A relaxed cancellation condition according to another example (seventhexample) is satisfied when the reliability of the detection result ofthe sensor 12 is reduced, and a specified steering operation wasperformed. In this case, it may be preferable not to continue automaticbraking; therefore, the relaxed cancellation condition is established soas to make it more likely to cancel automatic braking. For example, whena laser sensor is used as the sensor 12, reduction of the reliability ofthe detection result of the sensor 12 may be detected when a temporaryreduction of reflection power of the laser sensor is detected.Generally, a temporary reduction of the reflection power of the lasersensor occurs when a detection beam of the reflection power changes froma main beam to a side beam as the distance between the forward obstacleand the vehicle decreases. While the detection beam of the reflectionpower changes from the main beam to the side beam when the distancebetween the forward obstacle and the vehicle becomes a very smalldistance (e.g., 3, 4 m), no temporary significant reduction in thereflection power of the laser sensor occurs when the detection result ofthe laser sensor has a high reliability. Accordingly, the temporarysignificant reduction in the reflection power of the laser sensor meanslow reliability of the detection result of the laser sensor. Similarly,the specified steering operation may be an operation that results in achange of the steering angle by a predetermined degree or larger. Thepredetermined degree of turn of the steering wheel may correspond to thelower limit of the range of steering angle within which the vehicle canmove in the lateral direction by a distance corresponding to the widthof one vehicle (or the width of one lane or the width of an overlaprange between the forward obstacle and the vehicle), within a shorttime. The predetermined degree may be set by experiment, or the like.Also, the specified steering operation may be a steering operation thatresults in an increase of the accelerator operation amount. Also, thespecified steering operation may be determined in view of the steeringtorque or steering speed. Also, the specified steering operation may bedetermined in view of the steering direction, as in the case of theninth example as described later.

A relaxed cancellation condition according to another example (eighthexample) is satisfied when the forward obstacle suddenly moved into thesame lane as that in which the vehicle is present (cutting-in of theforward obstacle or cutting-in of the vehicle occurs), and a specifiedsteering operation was performed after (in particular, immediatelyafter) the cutting-in. This is because, in this case, it can bedetermined that the driver performs a collision avoidance operation inresponse to cutting-in of the forward obstacle or after intentionalcutting-in of the vehicle. For example, the intentional cutting-in ofthe vehicle may take place when the vehicle cuts into pace between twovehicles running on a lane on the right-hand side of the vehicle inorder to pass through the space between the two vehicles and enter intoa right turn lane. Similarly, the specified steering operation may be anoperation that results in a change of the steering angle by apredetermined degree or larger. The predetermined degree of turn of thesteering wheel may correspond to the lower limit of the range ofsteering angle within which the vehicle can move in the lateraldirection by a distance corresponding to the width of one vehicle (orthe width of one lane or the width of an overlap range between theforward obstacle and the vehicle), within a short time. Thepredetermined degree may be set by experiment, or the like. Also, thespecified steering operation may be a steering operation that results inan increase of the accelerator operation amount. Also, the specifiedsteering operation may be determined in view of the steering torque orsteering speed. Also, the specified steering operation may be determinedin view of the steering direction, as in the case of the ninth exampleas described later. The steering direction may be the same direction asthe steering direction at the time of cutting-in. When this relaxedcancellation condition is used in step S208 of FIG. 2, the informationfrom the sensor 12, and the steering angle information, may be obtainedas sensor information in step 200. The cutting-in of the forwardobstacle or the cutting-in of the vehicle may be detected based on thevehicle lane probability (probability with which the forward obstacleexists in the same lane as the vehicle) calculated based on theinformation from the sensor 12. For example, the vehicle laneprobability may be computed by accumulating the probability with whichthe forward obstacle exists in the same lane as the vehicle, at giventime intervals, (for example, accumulating 5% at a maximum at given timeintervals, up to 100% at a maximum as the upper limit of the accumulatedvalue). This manner of calculation is based on the same way of thinkingas that about a ballot box which will be described later. In this case,when the vehicle lane probability rises sharply, it may be determinedthat cutting-in of the forward obstacle or cutting-in of the vehicleoccurred.

A relaxed cancellation condition according to another example (ninthexample) is satisfied when the forward obstacle overlapped the vehiclesuch that the centerline of the forward obstacle deviated to the rightor to the left in the lateral direction from that of the vehicle(namely, the overlap percentage is smaller than 100%, as shown in FIG.4A), and a specified steering operation was performed in such adirection as to reduce the overlap range. This is because, in this case,a collision avoidance operation can be more easily performed as comparedwith the case where the lateral position of the forward obstaclecoincides with that of the vehicle (namely, the overlap percentage is100%, as shown in FIG. 4B), and it can be determined that the driverperforms the collision avoidance operation. In the example as shown inFIG. 4A, this relaxed cancellation condition is satisfied when thespecified steering operation to turn the vehicle to the right isperformed. When this relaxed cancellation condition is used in step S208of FIG. 2, the information from the sensor 12, and the steering angleinformation, may be obtained as sensor information in step S200. Theoverlap percentage (range) may be calculated based on the informationfrom the sensor 12. Namely, the overlap percentage may be calculatedbased on the lateral position of the forward obstacle. At this time, amovement vector (see FIG. 5) of the forward obstacle may be taken intoconsideration. Similarly, the specified steering operation may be anoperation that results in a change of the steering angle by apredetermined degree or larger. The predetermined degree of turn of thesteering wheel may correspond to the lower limit of the range ofsteering angle within which the vehicle can move in the lateraldirection by a distance corresponding to the width of one vehicle (orthe width of one lane or the width of an overlap range between theforward obstacle and the vehicle), within a short time. Thepredetermined degree may be set by experiment, or the like. Also, thespecified steering operation may be a steering operation that results inan increase of the accelerator operation amount. Also, the specifiedsteering operation may be determined in view of the steering torque orsteering speed. Also, space for evacuation (e.g., the presence orabsence of a lane or a road shoulder) in a steering direction of thespecified steering operation may be taken into consideration, based onmap data of a navigation system, or information from a forward camera,for example.

A relaxed cancellation condition according to another example (tenthexample) is satisfied when a region (lateral position of collision) ofthe vehicle expected to collide with a forward obstacle was locatedcloser to one of the right and left sides of the vehicle as viewed inthe lateral direction, and a specified steering operation to turn thevehicle to the side opposite to the above one side was performed. Therelaxed cancellation condition according to the tenth example issubstantially based on the same way of thinking as the relaxedcancellation condition according to the ninth example as describedabove.

FIG. 5 illustrates one example of method for determining the relaxedcancellation condition according to the tenth example. In FIG. 5, amovement vector 72 is depicted along with the vehicle. The movementvector 72 is that of the forward obstacle located in front of thevehicle, and may be derived from positional information (informationfrom the sensor 12) of the forward obstacle obtained at a plurality ofpoints in time.

In FIG. 5, four ballot boxes 101, 102, 103, 104 are schematically shownin the front of the vehicle. The ballot boxes 101, 102, 103, 104corresponding to respective regions into which the front of the vehicleis divided in the lateral direction are virtually set. The number ofballot boxes (four in this embodiment) may be set to any number. Thewidth of each region in the front of the vehicle (namely, the width ofeach region corresponding to each ballot box) may be equal, or may beset in a different manner depending on the region.

In the example as shown in FIG. 5, the collision probability iscalculated for each region in the front of the vehicle. Here, thecollision probability is calculated for each region in the front of thevehicle, in each given cycle (e.g., in each control cycle shown in FIG.2), to be equal to 10% at a maximum. The collision probabilitycalculated for each region in the front of the vehicle is cast into oneof the ballot boxes 101, 102, 103, 104 corresponding to the region, ineach given cycle, and an accumulated value of the collisionprobabilities obtained in a total of ten cycles (the latest ten cycles)is evaluated. Namely, the accumulated value of the collisionprobabilities obtained at respective points in time, i.e., the latestten points in time, is evaluated. The collision probability at a certainpoint in time may be calculated based on the movement vector and thereliability. More specifically, which of the regions in the front of thevehicle to which the collision lateral position calculated based on themovement vector as described above belongs is determined, and aprobability of 10% at a maximum is given to the ballot box associatedwith the region to which the collision lateral position belongs. At thistime, the reliability may be taken into consideration in such a mannerthat the collision probability at that point in time is multiplied bythe degree of reliability at that point in time (reliability concerningthe calculated movement vector). For example, if the reliability at thatpoint in time is equal to the maximum value (e.g., 100%), the maximumprobability 10% (10%×1) may be given to the ballot box associated withthe region to which the collision lateral position belongs. If, on theother hand, the reliability at that point in time is equal to theminimum value (e.g., 0%), a probability of 0% (10%×0) may be given tothe ballot box associated with the region to which the collision lateralposition belongs.

In the example as shown in FIG. 5, a condition where the collisionprobabilities calculated at four points in time are cast into eachballot box is schematically illustrated. Collision probabilities largerthan 0(%) are cast at three points in time, into the ballot box 101, andcollision probabilities larger than 0(%) are cast at four points intime, into the ballot box 102, while collision probabilities larger than0(%) are cast at two points in time, into the ballot box 103, and nocollision probability larger than 0(%) is cast into the ballot box 104.For example, if the collision probabilities of 10% are cast into theballot box 102, at all of the latest four points in time (the collisionprobability is 0% at six points prior to the latest four points intime), the accumulated value of the collision probabilities of theballot box 102 becomes equal to 40%. Accordingly, in this case where theregion of the vehicle expected to collide with the forward obstacle islocated closer to the left side of the vehicle, the relaxed cancellationcondition according to the tenth example is satisfied when the specifiedsteering operation to turn the vehicle to the right is performed.Similarly, the specified steering operation may be an operation thatresults in a change of the steering angle by a predetermined degree orlarger. The predetermined degree of turn of the steering wheel maycorrespond to the lower limit of the range of steering angle withinwhich the vehicle can move in the lateral direction by a distancecorresponding to the width of one vehicle (or the width of one lane orthe width of an overlap range between the forward obstacle and thevehicle), within a short time. The predetermined degree may be set byexperiment, or the like. Also, the specified steering operation may be asteering operation that results in an increase of the acceleratoroperation amount. Also, the specified steering operation may bedetermined in view of the steering torque or steering speed. Also, spacefor evacuation (e.g., the presence or absence of a lane or a roadshoulder) in a steering direction of the specified steering operationmay be taken into consideration, based on map data of a navigationsystem, or information from a forward camera, for example.

While one embodiment of the invention has been described in detail, theinvention is not limited to any particular embodiment, but may beembodied with various modifications or changes, within the range asdefined by the appended claims. It is also possible to combine all of ortwo or more of constituent elements of the embodiment as describedabove.

For example, in the above-described embodiment, a part or all of thefunctions of the collision determination ECU 10 may be implemented byother ECU(s). For example, the processing illustrated in FIG. 2 may beexecuted by the brake ECU 20, or the collision determination ECU 10 maycooperate with the brake ECU 20 to execute the processing of FIG. 2.

While the above-described embodiment is concerned with cancellation ofautomatic braking, the invention may be applied to cancellation of alarmoutput. Namely, the invention may be applied to a vehicle control systemconfigured to perform alarm output, in place of automatic braking. Inthis case, if an alarm generation condition similar to and correspondingto the automatic braking condition is satisfied, a signal requestinggeneration of an alarm is generated, and an alarm is given to thedriver, based on this signal. Then, if a similar normal cancellationcondition or relaxed cancellation condition is satisfied, the collisiondetermination ECU 10 stops generating the signal requesting generationof an alarm. Also, if a similar alarm termination conditioncorresponding to the automatic braking termination condition issatisfied, output of the signal may be stopped. The way of thinkingabout the relaxed cancellation condition for stopping output of thesignal requesting generation of an alarm may be similar to that aboutthe relaxed cancellation condition for stopping output of the signalrequesting execution of automatic braking.

In the above-described embodiment, an alarm may be generated in anymanner, along with automatic braking. In this case, a relaxedcancellation condition may be satisfied when a specified steeringoperation, an increase in the depression amount of the acceleratorpedal, or re-depression of the accelerator pedal, is detected within agiven period of time after the alarm starts being generated.

While the sensor 12 of the above-described embodiment is designed todetect a forward obstacle located in front of the vehicle, the sensor ofthe invention may detect an obstacle, such as a rear obstacle or a sideobstacle, other than the forward obstacle. For example, the sensor maybe in the form of a rear radar sensor that detects a rear obstacle, or aside radar sensor that detects a side obstacle. Namely, the obstacle maybe located in any direction.

While the above-described embodiment is concerned with cancellation ofautomatic braking control, the invention may be applied to cancellationof other control that may be executed so as to reduce damage at the timeof collision. Other control may include control for rewinding apre-crash seat belt (seat-belt pretensioner), control for moving theposition of a bumper, or the like, and others.

In the above-described embodiment, the automatic braking control mayinclude preliminary braking control executed prior to main automaticbraking control. Namely, the automatic braking control may be performedin such a manner that light, gentle braking force is generated at first,and then, required braking force is generated. Also, the automaticbraking control may be replaced with driving force suppression controlfor suppressing driving force by reducing the output of an engine ormotor, or may be implemented in combination with the driving forcesuppression control.

In the above-described embodiment, in connection with various types ofrelaxed cancellation conditions, a shift-lever operation to change theshift range to a lower range (e.g., from the fifth speed to the thirdspeed), or the like, may be additionally taken into consideration, fromthe same standpoint as the operation to increase the acceleratoroperation amount.

While the accelerator operation amount is determined by the amount ofoperation of the accelerator pedal in the above-described embodiment, itmay be equivalently determined by the throttle opening.

The invention claimed is:
 1. A vehicle control method of performingautomatic braking for automatically braking a vehicle or alarm output,depending on a likelihood of a collision between the vehicle and anobstacle, wherein said automatic braking or said alarm output iscancelled when one of a first cancellation condition and a secondcancellation condition is fulfilled during said automatic braking orsaid alarm output, the method comprising: determining the likelihood ofthe collision between the vehicle and the obstacle; starting saidautomatic braking in response to a determination that the likelihood ofthe collision is above a collision threshold value; cancelling saidautomatic braking or the alarm output according to a first cancellationcondition, wherein the first cancellation condition is fulfilled when anaccelerator operation amount is equal to or larger than a predeterminedthreshold value, during the automatic braking or the alarm output; andcancelling said automatic braking or the alarm output according to asecond cancellation condition other than the first cancellationcondition, wherein the second cancellation condition is fulfilled when asteering operation is detected under a situation where the acceleratoroperation amount of the vehicle is smaller than the predeterminedthreshold value, during the automatic braking or the alarm output whilethe likelihood of the collision between the vehicle and the obstacle isabove the collision threshold value.
 2. The vehicle control methodaccording to claim 1, wherein the second cancellation condition isfulfilled based on a combination of an accelerator operation thatincreases the accelerator operation amount and the steering operation.3. The vehicle control method according to claim 1, wherein the secondcancellation condition is fulfilled under a situation where (i) anoverlap range between the vehicle and the obstacle in a lateraldirection is located closer to one of right and left sides of thevehicle, and (ii) the steering operation includes turning the vehicle ina direction that reduces the overlap range.
 4. The vehicle controlmethod according to claim 1, wherein the second cancellation conditionis fulfilled based on a combination of a condition of the driver's facedetermined based on an image recognition result of a face image of thedriver and the steering operation.
 5. The vehicle control methodaccording to claim 4, wherein the second cancellation condition isfulfilled when the steering operation is performed after the driverchanges to face front from a condition where the driver fails to facefront, or after the driver's condition changes from a condition ofslumber into a condition of wakefulness.
 6. The vehicle control methodaccording to claim 1, wherein the steering operation includes anoperation that results in a change in a steering angle by apredetermined degree or larger.
 7. The vehicle control method accordingto claim 1, wherein the steering operation is determined based upon asteering torque or a steering speed.
 8. The vehicle control methodaccording to claim 1, wherein the automatic braking includes generationof braking force by controlling a brake system of the vehicle.
 9. Thevehicle control method according to claim 1, wherein the automaticbraking includes increasing a wheel cylinder pressure of each wheelunder a situation where a brake pedal is not operated.
 10. The vehiclecontrol method according to claim 1, wherein the automatic brakingincludes suppression of a driving force by reducing an output of anengine or a motor.
 11. A vehicle control system comprising: a sensorconfigured to detect a condition of an obstacle around a vehicle; anaccelerator pedal position sensor configured to detect an operationamount of an accelerator pedal; and an electronic control unit (ECU)configured to: determine a likelihood of a collision between the vehicleand the obstacle based on said condition, output a signal that requestsautomatic braking for automatically braking the vehicle or generation ofan alarm in response to a determination that the likelihood of thecollision is above a collision threshold value, stop output of thesignal according to a first cancellation condition, wherein the firstcancellation condition is fulfilled when the operation amount of theaccelerator pedal is equal to or larger than a first threshold value,and stop the output of the signal according to a second cancellationcondition other than the first cancellation condition, wherein thesecond cancellation condition is fulfilled when a steering operation isdetected under a situation where the accelerator operation amount of thevehicle is smaller than the first threshold value while the likelihoodof the collision is above the collision threshold value.